1. Field of the Invention
The present invention relates to treating and/or preventing heparinoid-induced autoimmune responses with certain dermatan sulfates and/or certain O-desulfated heparins. The present application particularly relates to the treatment and/or prevention of heparin-induced thrombocytopenia (HIT) and its associated disease states with certain dermatan sulfate and/or certain O-desulfated heparin HIT antagonists.
2. Related Art
Heparin and related heparinoids are sulfated mucopolysaccharides that belong to the family of glycosaminoglycans (GAGs). Over one trillion units of heparin are administered to 12 million patients annually in the United States for the prevention and treatment of thrombo-embolic diseases. See Fahey, “Heparin-Induced Thrombocytopenia.” J. Vasc. Nurs. (1995) 13:112-116; http://www.argatroban.com/ref 01htm, 2004. Cardiovascular-related thrombo-embolic diseases are among the leading causes of death in the United States. With perhaps the exception of stroke, the most widely prescribed anticoagulant for the prevention and treatment of these diseases is heparin. Heparin is ubiquitous throughout hospitals and is used routinely to keep all intravenous and other access lines to the patient from clotting.
While bleeding is a well understood side-effect of heparin, its use is also associated with a drug-induced, autoimmune hypersensitivity response that, paradoxically, predisposes the patient to develop severe thrombocytopenia and thrombosis, and is typically referred to as heparin-induced thrombocytopenia (HIT). The cardiology patient (e.g., a patient undergoing cardiopulmonary bypass surgery) is particularly predisposed to HIT because multiple exposures to heparin can occur prior to surgery that sensitize the patient to the high doses of heparin required to suppress the massive hypercoagulation response to surgery. See Bauer et al., “Prevalence of Heparin-Associated Antibodies without Thrombosis in Patients Undergoing Cardiopulmonary Bypass Surgery,” Circulation (1997) 95:1242-46; Pouplard et al., “Antibodies to Platelet Factor 4-Heparin After Cardiopulmonary Bypass in Patients Anticoagulated with Unfractionated Heparin or a Low Molecular Weight Heparin: Clinical Implications for Heparin-Induced Thrombocytopenia,” Circulation (1999) 99:2536-39; Trossaert et al., “High Incidence of Anti-Heparin/Platelet Factor 4 Antibodies After Cardiopulmonary Bypass surgery,” Br. J. Haematol. (1998) 101(4):653-55; Utley, “Cardiopulmonary Bypass Surgery,” Curr. Opin. Cardiol. (1992) 7(2):267-75.
Approximately 2-5% of all patients in the U.S. exposed to heparin develop an antibody-mediated hypersensitivity to heparin with associated thrombocytopenia, referred to as Type II HIT, with a significantly greater percentage developing antibodies without thrombocytopenia. See Wallis et al., “Failure of Early Heparin Cessation as Treatment for Heparin-Induced Thrombocytopenia,” Am. J. Med. (1999) 106(6): 629-635; Warkentin et al., “A 14-Year Study of Heparin-Induced Thrombocytopenia,” Am. J. Med. (1996) 101:502-507; Brieger et al., “Heparin-Induced Thrombocytopenia,” J. Am. Coll. Cardiol. (1998) 31:1449-1459. HIT disease can range from clinically insignificant to extremely severe. In contrast to the hemorrhagic thrombocytopenia disease states, HIT is associated with an increased risk of thrombosis. Historically, about 40% of these HIT patients develop a life-threatening thrombosis or HITT syndrome that produces devastating complications including necrosis of the extremities, stroke, myocardial infarction and pulmonary embolism. See Pouplard et al, supra; Trossaert et al, supra. Morbidity rates among HIT patients can reach as high as 61%, including a limb amputation rate of approximately 20% and an overall mortality rate of approximately 30%. See Silver et al., “Heparin-Induced Thrombocytopenia, Thrombosis, and Hemorrhage,” Ann. Surg. (1983) 198: 301-306; King et al., “Heparin-Associated Thrombocytopenia,” Ann. Intern. Med. (1984) 100:535-40; Utley, supra; Wallis et al., supra.
HIT can occur relatively rapidly after exposure to heparin. In a recent study, the onset of HIT occurred on or after day 4 of heparin therapy in 70% of patients; an even more rapid onset of HIT occurred in 30% of these patients, i.e., after 10.5 hours of heparin exposure. See Warkentin et al, “Temporal Aspects of Heparin-Induced Thrombocytopenia,” N. Eng. J. Med. (2001) 344: 1286-1292. Diagnosis is often based on a decline in platelet numbers and the exclusion of other causes of thrombocytopenia.
The prothrombotic state of HIT is caused in part by an immunologic reaction to heparin exposure that promotes platelet activation antecedent to thrombocytopenia and thrombosis. The immunological response to heparin exposure may also damage the endothelial cells that form the vascular lining and induce Tissue Factor expression in monocytes, thereby further enhancing the procoagulant state. See Visentin et al., “Antibodies from Patients with Heparin-Induced Thrombocytopenia/Thrombosis Are Specific for Platelet Factor 4 Complexed with Heparin or Bound to Endothelial Cells,” J. Clin. Invest. (1994) 93:81-88; Blank et al., “Anti-Platelet Factor 4/Heparin Antibodies from Patients with Heparin-Induced Thrombocytopenia Provoke Direct Activation of Microvascular Endothelial Cells,” Int. Immunol. (2002) 14:121-29; Pouplard et al., “Induction of Monocyte Tissue Factor Expression by Antibodies to Heparin-Platelet Factor 4 Complexes Developed in Heparin-Induced Thrombocytopenia,” Blood (2001) 97:3300-302.
Platelet activation is caused by an interaction of the heparinoid-induced immune complexes with the FcγIIa receptor on the cell surface. The major factors eliciting platelet activation with sera of HIT type II patients have previously been attributed to the degree of sulfation and molecular weight of the GAG, and not the type of glycosidic linkage of the oligosaccharide or the antithrombin III binding capacity of the GAG. Branched glucan sulfates form immune complexes with patient sera and activate platelets at lower concentrations than linear glucan sulfates. The suggested optimal size GAG for HIT antigen formation, immune complex formation and subsequent platelet activation is a hexadecasaccharide of 4800 Daltons. See Greinacher et al., “Heparin-Associated Thrombocytopenia: the Antibody Is Not Heparin Specific,” Thromb. Haemost. (1992) 67: 545-549; Greinacher et al., “Characterization of the Structural Requirements for a Carbohydrate Based Anticoagulant with a Reduced Risk of Inducing the Immunological Type of Heparin-Associated Thrombocytopenia,” Thromb. Haemost. (1995) 74: 886-892. Thus, it has been previously concluded that hyper- or oversulfation of GAGs is an inappropriate approach to anticoagulation based on the HIT inducing potential of sulfated GAGs, and that to reduce the ability of a GAG to induce a HIT response: (i) the nature of the glycosidic bond is unimportant; (ii) the molecule should be unbranched; (iii) the molecule should have a degree of sulfation (i.e., the number of sulfate groups/monosaccharide) of less than 0.60 (i.e., a sulfate to carboxylate (S/C) ratio of no more than 1.2) for chain lengths greater than 10 monosaccharides (i.e., greater than 3000 Daltons); (iv) the molecule should be smaller than 2400 Daltons if its degree of sulfation is 1.0-1.3; and (v) the therapeutic concentration should not exceed 0.12 μg/ml if the degree of sulfation is greater than 0.6 and the chain length greater than 2400 Daltons. See Greinacher et al., “Characterization of the Structural Requirements for a Carbohydrate Based Anticoagulant with a Reduced Risk of Inducing the Immunological Type of Heparin-Associated Thrombocytopenia,” Thromb. Haemost. (1995) 74: 886-92.
The antigenic complexes formed in HIT are comprised of heparin and releasable platelet proteins, predominantly platelet factor 4 (PF4), a platelet-specific heparin-binding protein. See Greinacher et al., “Heparin-Associated Thrombocytopenia: Isolation of the Antibody and Characterization of a Multimolecular PF4-Heparin Complex as Major Antigen,” Thromb. Haemost. (1994) 71: 247-51. Heparin and PF4 molecules assemble into a multimolecular antigenic complex. The binding of PF4 to heparin induces the formation of antigenic domains, or neoepitopes, on the PF4 surface that elicit an antibody-mediated immune response. See Li et al., “Defining a Second Epitope for Heparin-Induced Thrombocytopenia/Thrombosis Antibodies Using KKO, a Murine HIT-like Monoclonal Antibody,” Blood (2002) 99: 1230-36. The immune response is polyclonal and polyspecific with at least three neoepitopes identified based on immunoreactivity studies. See Suh et al., “Antibodies from Patients with Heparin-Induced Thrombocytopenia/Thrombosis Recognize Different Epitopes on Heparin:Platelet Factor 4,” Blood (1998) 91:916-22.
Antigenic complexes reactive to HIT antibodies can be formed between a variety of negatively charged polyanions and platelet proteins in vitro and in vivo. See U.S. Pat. No. 5,972,718 (Moghaddam et al.), issued Oct. 26, 1999, which discloses the formation of antigenic neoepitopes comprised of polymers bound to PF4 reactive with HIT antibodies, where the polymers can be polyvinyl sulfonate, polystyrene sulfonate, polyanetholesulfonate, polyvinyl phosphate, polyvinyl phosphonate or polyvinyl sulfate comprised of 10-60 subunits having molecular weights between 2000 and 6000; U.S. Pat. No. 5,972,717 (Aster et al.), issued Oct. 26, 1999, which discloses the formation of antigenic neoepitopes reactive with HIT antibodies in which the complexes expressing the antigenic neoepitopes are comprised of PF4 or peptides of PF4 bound to heparin, heparin fragments, heparin salts, heparamine, metallic heparinates, heparin sulfate, chondroitin sulfate, dermatan sulfate and keratan sulfates having preferably 10-20 saccharide residues; U.S. Pat. No. 5,466,582 (Amiral), issued Nov. 14, 1995, which discloses the formation of antigenic neoepitopes reactive with HIT antibodies in which the complexes expressing the antigenic neoepitopes are comprised of PF4, or peptides of PF4 bound to heparin, metal heparinates, heparinoids and heparin fragments, where the heparin fragments have an average molecular weight of less than 6000 Daltons, the heparinoids being selected from the class of heparamine and chondroitin sulfates. Twenty monosaccharides (approximately 6000 Daltons) of chondroitin sulfate represents the minimal chain length that binds PF4 whereas the affinity of chondroitin sulfate for PF4 increases with increased content of the disulfated disaccharide (→4 GlcAβ1→3GalNAc(4,6-O-sulfate) β1→). See Petersen et al., “Characterization of a Neutrophil Cell Surface Glycosaminoglycan that Mediates Binding of Platelet Factor 4,” J. Biol. Chem. (1999) 274: 12376-82. However, increased sulfation of chondroitin sulfate induces antibodies cross-reactive with the PF4-heparin complex, thrombocytopenia and thrombosis. See Greinacher et al., “Heparin-Associated Thrombocytopenia in a Patient Treated with Polysulphated Chondroitin Sulphate: Evidence for Immunological Crossreactivity between Heparin and Polysulphated Glycosaminoglycan,” Brit. J. Haematol. (1992) 81: 252-54.
Treatment of HIT usually involves heparin withdrawal and sometimes transfusion. Even so, the failure of early heparin cessation as a treatment for HIT has led to the approval of several direct thrombin inhibitors as alternative anticoagulants. Patients who are positive for the immune complex of heparin-IgG-PF4 or are subject to platelet loss or thrombosis while on heparin therapy are candidates for alternative anticoagulant therapies. Presently the thrombin inhibitors ACOVA™ (argatroban) and Refludan® (recombinant hirudin) are approved for the treatment of HIT/HITT where heparin is contraindicated. These drugs, however, have narrow therapeutic indices, lack antidotes and require laboratory monitoring. Even with the use of these approved drugs, circulating immune complexes may persist for days to weeks and continue to promote the immunohematologic prothrombotic state because these direct thrombin inhibitors do not eliminate all thrombosis associated with HIT. See Bauer et al., supra; http://www.argatroban.com/ref—0.1htm, 2004, supra; Walenga et al., “Combined Thrombin and Platelet Inhibition Treatment for HIT Patients,” Hämostaseologie (1999) 19:128-33; Greinacher et al., “Lepirudin (Recombinant Hirudin) for Parenteral Anticoagulation in Patients with Heparin-Induced Thrombocytopenia,” Circulation (1999) 100(6):587-93. As such, the predisposition to life-threatening thrombosis in HIT is neither predictable nor adequately addressed by the alternative use of these direct thrombin inhibitors. Accordingly, despite the use of these alternatives, the morbidity and mortality of HIT patients remains relatively high, and will likely remain so until a therapy is developed that treats the root cause of this disease initiated by the formation and action of the immune complexes in HIT which adversely modulate the functions of platelets, endothelial cells and monocytes.